I change out blades when needed. Some blades last longer than others. @Bama Samurai mentioned that the sweet spot is typically 3-7 shaves for most people, and I have to agree with that. I have, however, used a blade 20 times before...and transversely have thrown out a blade mid-shave on its very first use. I see no reason to change blades every shave regardless of price. It is simply a waste of our 2 most precious resources, time and money.